1. Field of the Invention
This invention relates to an image sensing device which permits highly accurate exposure control.
2. Description of the Prior Art
Heretofore, a device of this kind has been required to have an extremely high exposure control accuracy in taking a still picture of an object to be photographed since the response range of the image sensor is extremely narrow. Meanwhile, where an optical view finder of the TTL (through the lens) type is employed in the device of this kind, the diaphragm aperture of the device is preferably left in a full open state until immediately before photographing for the purpose of having a bright image plane within the view finder. Therefore, with the aperture in a full open state, light measurement is performed by means of a photometric element which is arranged separate from the image sensor and which has a wider dynamic range than the image sensor; and exposure control is performed on the basis of a photometric data thus obtained, so that exposure control can be quickly carried out after the start of photographing.
However, the photometric information thus obtained with the maximum aperture differs from photometric information obtained with the diaphragm aperture stopped down to a value used for actual photographing. It has been ascertained that this discrepancy in the photometric information is not ignorable in the case of an image sensor of a narrow dynamic range.
Furthermore, to solve the problem of the error or discrepancy between the photometic data obtained with the maximum aperture and the photometric data obtained with an actual stopped down aperture, it is conceivable to obtain accurate exposure data by driving the diaphragm and a shutter to have their values actually used immediately before an actual photo-taking operation. However, such an arrangement results in an extremely poor response which often causes the photographer to miss a desired shutter opportunity.
This invention is directed to the solution of the problems presented by the prior art devices. It is, therefore, an object of this invention to provide an image sensing device and an exposure control method, wherein exposure control may be accomplished with a high degree of accuracy by operating an image sensor under substantially the same exposure condition as the condition under which photographing is to be performed with the length of preparation time required for photographing shortened to a minimal time.
The above and further objects and features of this invention will become apparent from the following detailed description of a preferred embodiment thereof taken in conjunction with the accompanying drawings.